The present invention relates to a grip of a writing material which is installed near the tip of a shaft cylinder of the writing material and which can reduce the burden on user's fingers for a prolonged use of the writing material.
Some conventional writing materials include a cylindrical grip installed near the tip of shaft cylinder of the writing material which cylindrical grip consisting of an elastic material having concaves and convexes formed on its surface. The purpose of using the cylindrical grip is to reduce burdens on a user's fingers and to prevent the fingers from slipping readily on the shaft cylinder owing to moisture such as sweat, when the writing material is used for a long hours.
With the cylindrical grip consisting of the elastic material such as rubber and simply having concaves and convexes formed on its surface, even if the moisture of sweat on the fingers resulting from the long use of the writing material adheres to a surface of the grip, the user's fingers are locked on the concaves and convexes on the surface. Consequently, the writing material can be reliably gripped. However, if the cylindrical grip consisting of the elastic material such as rubber is thin, it is not readily deformed. When such writing material is used for a long time, pressure from the fingers is unlikely to be absorbed. Consequently, the long use of the writing material imposes burdens on the fingers, for example, makes the fingers numb, just as in the case of the direct gripping of the shaft cylinder of the writing material. In contrast, a thicker grip exerts a stronger force of restitution in response to the pressure from the fingers when the writing material is gripped. When the writing material is kept gripped for a long time against the force of restitution of the grip, the fingers must exert a stronger force than they otherwise need to do. This fatigues the user and thus imposes excessive burdens on the user.
Thus, the grips of writing materials just described below have been proposed which are elastic and which absorb the pressure from the fingers while being readily deformed during writing, thus avoiding imposing excessive burdens on the user.
For example, the grip installed near the tip of shaft cylinder of the writing material comprising a soft elastic member such as soft rubber or thermoplastic elastomer has been proposed. In this case, the pressure from the user's fingers during writing or the like is easily absorbed by deformation of the grip. However, since the soft elastic member such as soft rubber or thermoplastic elastomer is likely to be deformed, if it is installed in the shaft cylinder of the writing material, the pressure from the user's fingers during writing significantly deforms the writing material in the axial direction of the shaft cylinder. This readily shifts the positions of the fingers optimum for gripping the writing material. The user must thus frequently re-grip the writing material.
The grip of the writing material comprising a cylindrical shape memory resin in which silicone oil or other gel substance is sealed has been proposed. In this case, the pressure exerted during writing markedly deforms the grip in the axial direction of the shaft cylinder, thus readily shifting the original positions of the fingers optimum for the user, as in the case in which the grip is composed of the soft elastic member such as soft rubber or thermoplastic elastomer. Consequently, the user cannot reliably grip the writing material and must re-grip the wiring material many times during long writing. Furthermore, the grip requires a firm sealing structure that prevents the leakage of silicone oil or other gel material sealed in the grip. This makes the structure of the grip complicated and requires much attention to be paid to the material of the grip. As a result, manufacturing costs increase sharply.
Moreover, the grip of the writing material having a rib formed on an inner wall surface of a cylinder of a soft material and extending in the axial direction of the shaft cylinder, to create cavities inside areas against which the thumb, the index finger, and the middle finger abut has been proposed. In this case, deformation of the cavities absorbs the pressure from the fingers acting in the radial direction of the shaft cylinder when the writing material is gripped. However, when the user's fingers are positioned on the rib, which abuts against the surface of the shaft cylinder, the rib is pivoted along the circumference of the shaft cylinder depending on the magnitude of a force exerted by the user's fingers. Consequently, deformation of the grip is not uniform and it is possible that the user cannot reliably grip the writing material with the user fingers placed at desired positions.
Furthermore, the grip formed like cylinders having an inner peripheral surface fitted on an outer peripheral surface of a gripped area of the shaft cylinder, a plurality of a hollow portions formed in a peripheral wall of the cylinder so as to penetrate the cylinder in its axial direction and arranged along a circumference of the shaft cylinder and a ventilation passage formed at an end of the grip to allow the communication between the hollow portions and the exterior has been proposed. In this case, air moves freely to and from the exterior through the ventilation passage. Accordingly, even if the user exerts a force on the grip with his or her fingers during writing, the hollow portions can be readily deformed to absorb the pressure. However, the plurality of hollow portions, arranged in parallel along the circumference of the shaft cylinder, are separated from one another by a support portion. Thus, in the hollow portions, air can flow easily in the axial direction of the shaft cylinder but not along the circumference of the shaft cylinder. As a result, the support portion, which separates the hollow portions from one another, repels the pressure from the user's fingers. This makes deformation of the grip nonuniform as previously described. In particular, since the hollow portions are formed in the axial direction of the axial shaft, the positions of the user's fingers are likely to be shifted downward during use. Thus, when the user keeps on writing for a long hours, the user cannot reliably grip the writing material and thus exerts an unnecessary force. This results in excessive burdens on the user's fingers.
A problem with the prior art is that during writing, notably during long writing, the user cannot grip the writing material at the optimum positions. It is thus an object of the present invention to allow the grip of the writing material to be optimally deformed with respect to the positions of the user's fingers, at which the writing material is directly gripped, and in response to the pressure from the fingers or the like and remain in the deformed state.